It is known to use automated spray applicators to apply coatings of various types on objects during manufacture. Automobile vehicle bodies commonly are coated using robotic devices with spray applicators. The robot is programmed to perform a sequence of maneuvers and adjustments so that the vehicle body pieces are adequately and precisely covered in a rapid procedure with minimal waste.
To reduce the amount of over spray and further reduce waste, it is known to use atomizing applicators. A bell cup rotates at high speed, and the coating material, such as paint, is provided to the inside of the cup. As the paint or other coating moves outwardly and off the cup surface as a result of centrifugal force, the coating is atomized into a fine mist and directed at the object to be coated. It is known to use shaping air streams to confine and direct the atomized coating toward the object. It is also known to charge the atomized mist with electrical potential and to ground the object being coated so that the coating material is attracted to the object, further reducing over spray and improving coverage on irregularly shaped target objects.
In present day manufacturing procedures, such as for automobile vehicle bodies, it is common to have parts in random color sequences advancing along a manufacturing line. Thus, for each object to be coated it may be necessary to change the color of paint or other coating used from that used for the previous object. To ensure purity of the coating to be applied, it is necessary to clean at least parts of the coating applicator. It is also necessary to routinely clean the atomizer for continued proper operation.
A problem associated with known rotary atomizers is caused by the pumping effect of the bell cup rotating at high velocities. At such high speeds, the bell cup operates as an effective air pump, evacuating air from just behind the bell cup. Therefore, a low-pressure area exists immediately behind the bell cup and in front of the forward end of the applicator shroud. Surrounding air, which may contain atomized mist from the applicator, tends to fill the low-pressure area behind the bell cup. As a result, the back of the bell cup can become covered with coating in a relatively short period of time, necessitating cleaning. It is desirable to minimize the frequency of and time needed for cleaning. It is also desirable to minimize as much as possible the volume of cleaning agents required. For many coatings, the cleaning agents are considered hazardous waste and must be properly handled for disposal. Minimizing cleaning frequencies and reducing the amount of cleaning agent required can significantly decrease costs and increase productivity of a coating operation.
What is needed in the art is a simple yet effective system for reducing the low-pressure area created behind a rotating bell cup in an atomizing applicator.